Start structuring the package

[guilgautier]

Let's organize files according to Python standards.

• [x] add a .gitignore file see https://github.com/github/gitignore/blob/master/Python.gitignore
• [x] add a LICENCE file (basic MIT should be fine)
• [x] structure the project using src/ layout https://packaging.python.org/tutorials/packaging-projects/#uploading-your-project-to-pypi
• [x] add pyproject.toml file (replaces setup.py and requirements.txt)

More generally, I suggest we use poetry as a tool to manage dependencies and in a near future to release the package on PyPI. I'll show you how to work with it ;)

[guilgautier]

Reproductibility setup and Python workflow using poetry is ready. @dhawat is now familiar with it.